title: Expression of muscle-specific actins and myosin in light microscopically undifferentiated small and dark cell malignancies of soft tissues.
abstract: Eighteen light microscopically undifferentiated small and dark cell malignancies, previously studied ultrastructurally and immunohistochemically in terms of desmin, vimentin and myoglobin expression, were analyzed using mono- and polyclonal antibodies to muscle-specific isoforms of myosin and actin. For comparison, 10 characteristic rhabdomyosarcomas, 5 alveolar and 5 embryonal, were included in the study. A polyclonal antibody to skeletal myosin produced an indistinct staining in all the alveolar and embryonal rhabdomyosarcomas. The staining was most prominent in well-differentiated rhabdomyoblastic tumor cells. In the analysis of the small and dark cell malignancies, this antibody produced a weak and indistinct positivity which can not be interpreted with certainty as an expression of muscle-specific properties. An antibody directed at the alpha and gamma isoforms of actin, which are present in smooth and striated muscle, produced a distinct positive staining in all the alveolar and embryonal rhabdomyosarcomas and in 8/18 small and dark cell malignancies, 7 of which were also shown to express desmin. An antibody directed at the alfa-smooth muscle isoform of actin did not produce any positive staining in any of the tumors. The present study indicates that both muscle-specific actin and desmin can be expressed in tumors lacking ultrastructural evidence of a rhabdomyoblastic differentiation and that the combined use of monoclonal antibodies to desmin and muscle-specific actin is of value when it comes to recognizing rhabdomyosarcomas within the group of undifferentiated small and dark cell malignancies of soft tissue tumors.
authors.affiliation: Department of Pathology, University of Gothenburg, Sahlgren Hospital, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Seidal
authors.forename: L
authors.initials: L
authors.lastname: Angervall
authors.forename: L G
authors.initials: LG
authors.lastname: Kindblom
mesh_terms: D000199:Actins / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000378:metabolism* / Q000473:pathology; D003893:Desmin / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007382:Intermediate Filaments / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D009211:Myoglobin / Q000235:genetics / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D012208:Rhabdomyosarcoma / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D012983:Soft Tissue Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D014746:Vimentin / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D003893:Desmin; D009211:Myoglobin; D014746:Vimentin; D009218:Myosins